SCUBA diver proteome: Decompression stress vs. decompression sickness

Ezine

Published: Oct 1, 2017

Author: Steve Down

Channels: Proteomics & Genomics / Proteomics

Decompression sickness

One of the biggest risks to SCUBA divers, apart from being attacked by marine life, is decompression sickness (DCS). In its gravest form, it can kill but it can also cause severe debilitation of a diver due to cardiac problems and brain damage. Although it is most commonly associated with the production of nitrogen bubbles in the organs and joints as a diver ascends too quickly, these bubbles are not a guarantee of DCS. Other factors must be at play.

In a study published in 2016, a team of European scientists used proteomics techniques to see if the bodily proteins of rats were changed following the onset of DCS. They subjected the animals to a simulated air dive in a hyperbaric chamber followed by decompression to induce DCS and found changes affecting four proteins. Apolipoprotein A1, α1-antiproteinase and serine protease inhibitor A3K had altered abundances compared with asymptomatic animals and the abundance of the tetramer of transthyretin (but not its monomer) was reduced about 73-fold. This was proposed tentatively as a biomarker of DCS.

However, the team expressed caution. It is possible, they explained, that these protein changes were induced by the dive itself and not the onset of DCS. So, now they have extended their research on humans to see if the effects of decompression, without the onset of DCS, also cause the protein levels to change. The results were reported by Jacky Lautridou in Proteomics – Clinical Applications for the multinational study with scientists from France, Serbia, Canada, USA, Norway and Croatia.

Single SCUBA dive

Twelve healthy, experienced male divers volunteered for the study. They each undertook a single SCUBA dive in the sea to 18 m and stayed at that depth for 47 minutes while swimming at "moderate intensity." Then they ascended steadily over two minutes and were given echocardiograms to look for venous gas bubbles that confirmed decompression stress.

Blood samples were taken before the dive then 30 minutes and 2 hours after surfacing and the proteins in the plasma were separated by isoelectric focussing followed by SDS-PAGE. In total, 454 protein spots were aligned on the gels from all divers but none of them exhibited altered abundances.

The current method, which tested three different blood samples from each diver, was more sensitive than the earlier rat study in which only samples collected after the simulated dive were taken and compared for asymptomatic, DCS and control rats. Yet, there were no changes in protein abundances before and after the SCUBA dives.

So, the authors concluded that decompression stress, in the absence of decompression sickness, does not alter the human proteome. This, in turn, provides further support for the four proteins in the rat study as biomarkers of DCS.

Closer to biomarkers

An earlier study published in 2013 did find some changes in protein abundance in divers. The fact that these were not replicated in the current work might be a result of the more sensitive gene expression methods that were employed. But for asymptomatic divers who do not develop DCS, the researchers concluded that "the search for blood biomarkers, even with a high bubble grade, are unlikely to be successful."

The next stage in this project will be to check if the protein changes reported in the earlier study by Lautridou on rats can be translated to humans who contract DCS. If the transthyretin tetramer is implicated once again, the team plan to make this the focus of their efforts, partly due to the fact that it has previously been associated with inflammation and amyloid pathologies and also because of its vast change in concentration.

It is hoped that the results will eventually lead to better care of divers and possibly, people who undertake other activities that run the risk of developing DCS by undergoing fast changes in pressure. Astronauts performing spacewalks, high altitude pilots and tunnellers could also benefit from the results.